This invention relates to a check valve especially adapted for use on a fire engine pumper having a water reservoir with the reservoir adapted for being filled from a water source such as a fire hydrant or a large pond, i.e., a low pressure water supply.
In valves of this type, it is necessary that a large fluid flow area be provided to ensure little or no resistance to flow there-through. One such attempt at such a valve is discussed in U.S. Pat. No. 3,983,899. This valve is a spring-loaded check valve with a body having an inlet and an outlet coaxially aligned. The valve is urged closed by a check spring to ensure that the inlet fluid pressure must be sufficient to overcome any hydrostatic pressure in the fire engine reservoir before the valve will open. Furthermore, in order to prevent the check valve opening when the fire engine pumper dispenses water from the reservoir, and is not filling up the valve, it includes a locking mechanism for maintaining it closed so that the vacuum pull on the reservoir does not open it. Furthermore, by having a check spring which closes the valve, this valve reduces the "water hammer" effect which normally occurs when flow is suddenly shut off.
Nonetheless, this valve suffers from a number of disadvantages. For instance, when it becomes necessary to fill the first engine reservoir from a source of little or no water pressure, the valve will be maintained shut. Furthermore, the construction of this valve is such that after repeated openings and closings, the valve stem and body will suffer significant damage as a result of the "water hammer" effect, even though the damaging effects are reduced as compared to other valves. Moreover, when using this valve air often becomes trapped in the line between the valve and incoming water when flow is first commenced, thus creating difficulties in initial opening of the valve.
U.S. Pat. No. 2,856,958 teaches another construction of a prior art check valve. This valve includes a closing member which is urged to seal against a large inlet. However, this valve also includes all or more of the disadvantages of the above-discussed valve.